Does NASCAR skew the definition of a stock car?

F1 Sim Racer & #1 St. Bernard Lover on RDPremium Member

Toyota, Chevrolet and Ford provide teams with their pre-designed cars. NASCAR is technically a Formula sport in that it does not allow technology that gives a competitive advantage.

My point is, don't these cars defeat the definition of a true stock car? If a stock car has some kind of technology that allows for a competitive advantage, then, that is a true stock car as long as it came from the mechanic himself/herself.